Method of producing steel sections of improved quality

Abstract

A steel section 6 to 40 mm thick, emerging from a hot rolling mill at 1000° to 800° C. is surface quenched for 2 to 6 seconds at a cooling rate of the order of 1.5 to 5 MW/m 2 . During subsequent self-tempering of the quenched surface by heat from the remainder, the section tends to an equalization temperature of 500° to 700° C.

We claim: 
     
       1. A method of improving the quality of a steel section having a thickness of 6 to 40 mm, emerging from a hot rolling mill at a temperature of 1000° to 800° C., the method comprising subjecting the section to surface quenching for 2 to 6 seconds, wherein the cooling rate during the surface quenching is of the order of 1.5 to 5 MW/m 2 , and the equalization temperature of the section due to subsequent self-tempering is 500° to 700° C. 
     
     
       2. A method as claimed in claim 1, in which the steel contains 0.11 to 0.20% carbon, 0.5 to 1.1% manganese, 0.20 to 0.40% silicon, and 0.018 to 0.040% aluminium. 
     
     
       3. A method as claimed in claim 1 or 2, in which the steel is semi-killed steel containing 0.11 to 0.20% carbon, 0.5 to 1.1% manganese, 0.20 to 0.40% silicon, and 0.018 to 0.040% aluminium. 
     
     
       4. A method as claimed in claim 1, in which the steel is aluminium killed steel containing 0.05 to 0.20% carbon, 0.20 to 0.40% silicon, 1 to 2% manganese, and 0.018 to 0.040% aluminium. 
     
     
       5. A method as claimed in claim 4, in which the steel further contains 0.015 to 0.040% niobium. 
     
     
       6. A method as claimed in claim 1, in which the steel contains 0.05 to 0.20% carbon, 0.20 to 0.40% silicon, 1 to 2% manganese, 0.018 to 0.040% aluminium, max. 0.06% niobium, and 0.04 to 0.20% vanadium.